The .375 Weatherby Magnum is a .37 caliber (9.5 mm) rifle cartridge. The cartridge is a blown out, improved and provided with the Weatherby double radius shoulder – given the Weatherby treatment – version of the .375 H&H Magnum. Unlike other improved versions of the .375 H&H Magnum like the .375 Ackley Improved, the .375 Weatherby Magnum is not a wildcat and existed as a proprietary cartridge until the CIP published specifications for the cartridge.